Effect of metal-ion-to-fuel ratio on the phase formation of bioceramic phosphates synthesized by self-propagating combustion

Abstract

Synthetic calcium hydroxyapatite (HAP, Ca 10 (PO 4 ) 6 (OH) 2 ) is a well-known bioceramic material used in orthopedic and dental applications because of its excellent biocompatibility and bone-bonding ability due to its structural and compositional similarity to human bone. Here we report, for the first time, the synthesis of HAP by combustion employing tartaric acid as a fuel. Calcium nitrate is used as the source of calcium and diammonium hydrogen phosphate serves as the source of phosphate ions. Reaction processing parameters such as the pH, fuel-oxidant ratio and autoignition temperature are controlled and monitored. The products were characterized by powder x-ray diffraction, which revealed the formation of a hexagonal hydroxyapatite phase. Fourier transform infrared spectroscopy (FT-IR) spectra showed that the substitution of a carbonate ion occurs at the phosphate site. The morphology of the particles was imaged by scanning electron microscopy, which also revealed that the particles are of submicron size. Thermal analysis showed that the phase formation takes place at the time of combustion. Surface area and porosity analysis showed that the surface area is high and that the pores are of nanometer size. The mean grain size of the HAP powder, determined by the Debye-Scherrer formula, is in the range 20-30 nm. Chemical analyses to determine the Ca : P atomic ratio in synthesized ceramics were performed, and it was found to be 1 : 1.66.

Influence of fuels and combustion aids on solution combustion synthesis of bi-phasic calcium phosphates (BCP)

“…Sasikumar et al have synthesized HA using tartaric acid [12], succinic acid and citric acid [13] as fuels. It was suggested that the mentioned fuels acted as complexing agents reacting with metal cations, and prevented selective precipitation at the heating stage of solution.…”

“…It was also detected that fuel to oxidizer ratio influenced on combustion temperature. In various works [8,10,12,13,16,17] concentrated nitric acid was added in the initial solution to obtain transparent solution (without precipitates). In all cases it was not given attention to the presence of HNO 3 and its effect on the combustion process and yielded products.…”

Calcium deficiency in hydroxyapatite and its drug delivery applications

“…Further, the band at 961 cm −1 corresponding to the m1 vibrational mode of a phosphate group, can be observed in all spectra of CDHAP and the weak band at 473 cm −1 is attributed to the m2 vibrational mode of the phosphate group. Especially, phosphate m4 bands were observed at 633, 602 and 565 cm −1 [9, 10]. We did not observe much difference in the FTIR spectra of all CDHAPs, but a small shift in the stretching vibration of the −OH group may be due to the calcium deficiency in the HAP structure.…”

“…The shift in the major intensity peak [2 θ value 32.0/(211) plane] suggests that the calcium deficiency has occurred in HAP structure. For x = 0.3, one extra peak at a 2 θ value of 31.30 was found, indicating the formation of β‐tricalcium phosphate as an impurity [9, 10]. This clearly indicates that the structure is not stable at x = 0.3.…”

Structural and proton transport studies on nanocrystalline [Ca10(PO4)6(OH)2] (HAp), HAp–Nafion® composite, and natural human bone

“…Since microstructure differs from the method of preparation, various synthesis methods such as solid state reaction 8, hydrothermal 9, sol–gel 10, 11, co‐precipitation 12, flame spray pyrolysis 13, emulsion 14, mechanochemical 15, template 16, microwave 17, polymer‐assisted 18, self‐propagating combustion 19, 20, and sonochemical technique 21 have been reported for HAp synthesis. Recently, sonochemical method has been chosen to prepare a variety of nanostructured materials at room temperature.…”